Method for implementing continuous radio frequency (RF) alignment in advanced electronic warfare (EW) signal stimulation systems

ABSTRACT

A method for using a “B” channel of a dual channel measurement receiver as a transfer standard for power measurement, which may include in an exemplary embodiment: correlating measurements made with an “A” channel to measurements made with an RF Power Meter on one RF signal source, so that readings from the “A” channel are aligned to the RF Power Meter; aligning the “B” Channel to the “A” Channel (Transfer alignment of Channel B to the RF Power Meter), once the “A” channel has been aligned to read the same as the RF Power Meter; and using the “B” Channel as a transfer standard to measure all remaining RF signal sources in the system, on a time-line much faster than may be accomplished using a power meter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 11/640,364, entitled “METHOD FOR IMPLEMENTING CONTINUOUS RADIOFREQUENCY (RF) ALIGNMENT IN ADVANCED ELECTRONIC WARFARE (EW) SIGNALSTIMULATION SYSTEMS” to Jaklitsch, et al. filed on Dec. 18, 2006, ofcommon assignee to the present invention the contents of which areincorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to simulation systems, moreparticularly to electronic warfare (EW) simulation systems, and evenmore specifically, to the issue of aligning laboratory EW simulationsystems.

2. Related Art

Electronic warfare (EW) simulation systems in a laboratory must bealigned. These simulation systems may typically include multiple signalsources (such as, e.g., but not limited to, modulated microwavesynthesizers), in which each of these signal sources may be capable ofproducing time-interleaved microwave pulses of different frequencies andmodulation characteristics, so as to emulate the signal characteristicsof a multiplicity of radar emitters. The simulation systems may bearranged to output similar RF signals on multiple channels, withcontrolled differences in specific parameters between channels.

Such systems must be aligned in order to ensure that the signals thesesystems produce, on each channel, are accurately calibrated, withrespect to each other and with respect to absolute standards, across awide range of frequency and attenuation. Conventionally, with currenttechnology, these systems are typically aligned in amplitude (RF Power)only, and are not aligned to maintain specific phase relationships fromchannel to channel. Even so, the conventional alignment process is atime-consuming, tedious operation, and it is not at all uncommon to getreports from users that they spend more time aligning, than they dousing, these systems.

There is now an emerging need for improved EW simulation systems. Itwould be desirable that an EW simulation system be capable of producingmicrowave signal characteristics with known phase relationships betweensignal sources. This need implies that the alignment problem, alreadytime-consuming and tedious to the extent that it is a significantimpediment to system operation, must be extended to somehow supportalignment of phase across frequency. What is needed then is an improvedEW simulation system capable of overcoming shortcomings of conventionalsolutions.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, anexemplary feature of this invention may provide a comprehensive,automated method for aligning amplitude, phase, and time, for everysignal source in an EW simulator. The EW simulator may contain, in anexemplary embodiment, an arbitrary number of signal sources (such as,e.g., but not limited to, typically, 96 or more). A feature of anexemplary embodiment of the EW simulator may perform alignment on atime-line that permits every signal source in the system to be fullyaligned, at every possible frequency and at every possible attenuationstate, in, e.g., but not limited to, less than, or about equal to, 15minutes. In addition, the method disclosed herein, according to anexemplary embodiment, may provide a continuous, on-going alignment ofthe system so that signal characteristics may be constantly realigned(e.g., but not limited to, approximately once per second) to eliminateeffects of thermal drift.

According to an exemplary embodiment, a method of providing anintegrated approach to automated system alignment, may include:providing amplifier compression alignment, (which may includecharacterizing and/or compensating for a parasitic effect); providingcontinuous internal alignment of phase and amplitude of a syntheticstimulus instrument (SSI) output signal; providing external measurementport alignment; and providing transfer alignment of internal measurementpaths.

According to one exemplary embodiment, the method may further includeproviding power leveling to improve accuracy.

According to one exemplary embodiment, the method may further includeproviding time angle of arrival alignment.

According to one exemplary embodiment, the method may further includeproviding pulse width alignment.

According to one exemplary embodiment, the method may include providingcontinuous internal alignment, which itself may include: a foregroundprocess, wherein the foreground process may include characterizing oneor more parameters that are most sensitive to fluctuation with at leastone of time and/or temperature, and updating the parameters for allfrequency at a high refresh rate; and a background process, where thebackground process may include characterizing one or more parametersthat are less sensitive to fluctuation with at least one of time and/ortemperature, and updating the parameters for all frequency at a lowerrefresh rate.

According to one exemplary embodiment, the method may include where theparameters may include base state phase and/or amplitude.

According to one exemplary embodiment, the method may further include aparametrically extendible measurement cycle, which may includematched-filter coherent measurement processing may include makingback-to-back elementary measurements, wherein each of the measurementsare phase offset by 180 degrees, to cancel a VSWR error.

According to one exemplary embodiment, the method may include providingamplifier compression alignment, which may include: characterizing theeffect of amplifier compression on phase and amplitude may include:driving an attenuation control as required to achieve actual attenuationstates in octave increments of dB, for each applicable range of stepattenuation; and measuring a super-attenuation and a saturation inducedphase contribution (SIPC) at each of the attenuation states, in each ofthe ranges of step attenuation.

According to one exemplary embodiment, the method may include drivingthe attenuation control as required to achieve actual attenuation statesin the octave increments, which may include: driving the attenuationcontrol as required to achieve actual attenuation states in the octaveincrements of dB may include at least one of 0, 0.25, 0.5, 1.0, 2.0,4.0, 8.0, and/or 16.0.

According to one exemplary embodiment, a method of characterizing theeffect of each step attenuator state, on phase and amplitude, mayinclude activating each step attenuator state as the sole contributor toattenuation, and measuring at least one of a step attenuator amplitudecontribution (SAAC) and/or a step attenuator phase contribution (SAPC).

According to one exemplary embodiment, a method for mapping an arbitraryRF Power command into hardware control signals used to produce acommanded RF Power at a Port output for each frequency, may include: a.providing a level shift that maps an absolute Power Command, in units ofdBm, to a relative power command, in units of dBfs; b. providing a stepattenuation state parser that computes the appropriate state for thestep attenuator, and subtracts a step attenuator amplitude contributionfrom the relative power command, to compute an AM DAC attenuation; c.providing a super-attenuation function that adjusts the AM DACattenuation command to produce desired attenuation, adding anyadditional attenuation as required to compensate for non-linear effectsof compression, wherein the super-attenuation function is implemented asa stored data table, in octave increments of dB, for each applicablerange of step attenuation, with an exact value determined by means ofquadratic interpolation at run time; d. providing a theoreticalconversion of the AM DAC attenuation command to hardware bits; and e.providing a frequency-dependent offset for power leveling.

According to one exemplary embodiment, the method may include providingthe super-attenuation function in the octave increments of dB, which mayinclude: providing the super-attenuation function in the octaveincrements of dB which may include at least one of 0, 0.25, 0.5, 1.0,2.0, 4.0, 8.0, and/or 16.0.

According to another exemplary embodiment, a method for mapping anarbitrary RF Phase Command into hardware phase-shift control signals, asrequired to produce a commanded RF Phase at the Port output for eachfrequency, may include: a. computing an aggregate Phase Compensationvalue from at least one of: i. a base-state phase error, measured ateach sub-band of a synthetic stimulus instrument (SSI), ii. a filterinduced phase contribution (FIPC) measured at closely spaced frequencyincrements across each sub-band, stored in data tables, and interpolatedat run-time using quadratic interpolation, iii. a step attenuator phasecontribution (SAPC), measured at each sub-band of the SSI, and/or iv. asaturation-induced phase contribution (SIPC), characterizing anon-linear phase shift associated with amplifier compression, whereinSIPC compensation is implemented as a stored data table, in octaveincrements of dB, for each applicable range of step attenuation, withthe exact value determined by means of quadratic interpolation at runtime; and b. subtracting the Phase Compensation value from the RF PhaseCommand.

According to one exemplary embodiment, the method may include where the(a) (ii) may include closely spaced frequency increments may includeabout 200 KHz.

According to one exemplary embodiment, the method may include where the(a) (iv) may include octave increments of dB may include at least one of0, 0.25, 0.5, 1.0, 2.0, 4.0, 8.0, and/or 16.0.

According to another exemplary embodiment, a method of using astate-estimation filter may include: using a state-estimation filter forcomputing true values for a step attenuator amplitude contribution(SAAC) and a step attenuator phase contribution (SAPC), in presence ofmeasurement noise.

According to one exemplary embodiment, the method may include where thestep attenuator amplitude contribution (SAAC) and the step attenuatorphase contribution (SAPC) may be computed as differentials from afull-power reference measurement may include amplitude and phase.

According to another exemplary embodiment, a method for using a “B”channel of a dual channel measurement receiver as a transfer standardfor power measurement may include: correlating measurements made with an“A” channel to measurements made with an RF Power Meter on one RF signalsource, so that readings from the “A” channel are aligned to the RFPower Meter; aligning the “B” Channel to the “A” Channel (Transferalignment of Channel B to the RF Power Meter), once the “A” channel hasbeen aligned to read the same as the RF Power Meter; and using the “B”Channel as a transfer standard to measure all remaining RF signalsources in the system, on a time-line much faster than may beaccomplished using a power meter.

According to another exemplary embodiment, a receiver apparatus mayinclude: a dual-channel coherent measurement receiver which may includeat least one internal channel operative to measuretime-division-multiplexed (TDM) feedback signals from each signal sourceof a synthetic stimulus instrument (SSI); and at least one externalchannel operative to make direct measurement at an external alignmentport output.

Further features and advantages of the invention, as well as thestructure and operation of various exemplary embodiments of theinvention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates exemplary SSI control parameters that may be used insome embodiments of the present invention.

FIG. 2 illustrates an exemplary overview of a function alignment thatmay be used in some embodiments of the present invention.

FIG. 3 is a block diagram illustrating an exemplary embodiment of themeasurement receiver that may be used in some embodiments of the presentinvention.

FIG. 4 illustrates an exemplary measurement cycle that may be used insome embodiments of the present invention.

FIG. 5 illustrates an exemplary matched filter measurement amplituderesponse that may be used in some embodiments of the present invention.

FIG. 6 illustrates an exemplary frequency sweep cycle that may be usedin some embodiments of the present invention.

FIG. 7 illustrates exemplary piece-wise interpolation groupings that maybe used in some embodiments of the present invention.

FIG. 8 illustrates an exemplary attenuation mapping function that may beused in some embodiments of the present invention.

FIG. 9 illustrates an exemplary phase mapping function that may be usedin some embodiments of the present invention.

FIG. 10 illustrates an exemplary time of arrival alignment pulsewaveform that may be used in some embodiments of the present invention.

DETAILED DESCRIPTION OF VARIOUS EXEMPLARY EMBODIMENTS OF THE INVENTIONOverview of an Exemplary Embodiment of the Present Invention

Exemplary embodiments of the invention are discussed in detail below. Indescribing exemplary embodiments, specific terminology may be employedfor the sake of clarity. However, the invention is not intended to belimited to the specific terminology so selected. While specificexemplary embodiments may be discussed, it should be understood thatthis is done for illustration purposes only. A person skilled in therelevant art will recognize that other components and configurations canbe used without parting from the spirit and scope of the invention.

Exemplary embodiments of the present invention may include apparatusesfor performing the operations herein. An apparatus may be speciallyconstructed for the desired purposes, or it may comprise a generalpurpose device selectively activated or reconfigured by a program storedin the device.

Exemplary embodiments of the invention may be implemented in one or acombination of hardware, firmware, and/or software. Exemplaryembodiments of the invention may also be implemented as instructionsstored on a machine-accessible medium, which may be read and executed bya computing platform to perform the operations described herein. Amachine-accessible medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-accessible medium may include readonly memory (ROM); random access memory (RAM); magnetic disk storagemedia; optical storage media; flash memory devices; electrical, optical,acoustical or other form of propagated signals (e.g., carrier waves,infrared signals, digital signals, etc.), and others.

FIG. 1 depicts a diagram 1000 illustrating an exemplary embodiment of anexemplary synthetic stimulus instrument (SSI) 1001, according to anexemplary embodiment of the present invention. Exemplary controlparameters for an exemplary RF signal source for an advanced electronicwarfare (EW) simulation system are illustrated in FIG. 1. Diagram 1000illustrates an exemplary simplified schematic of an exemplary particulartype of synthesized microwave signal generator, according to anexemplary embodiment, known as a synthetic stimulus instrument (SSI)1001. The basis of the SSI may be a direct digital synthesizer (DDS)1002. The DDS 1002 may be programmable, in frequency 1003 and phase 1004by digital means, and may thus be commanded to produce arbitrarymicrowave frequencies at arbitrary phase shifts, according to anexemplary embodiment.

The control for RF output power 1005 may be distributed throughout theRF distribution network, and may include, in an exemplary embodiment,three separate components: amplitude modulation (AM) digital to analogconverter (DAC) control 1006, power leveling control 1007, and a stepattenuator control 1008 (e.g., but not limited to, a 10 dB stepattenuator control 1008). The AM DAC control 1006 may provide fineamplitude modulation (AM) of the DDS output 1002 by multiplying thissignal 1010 with the output of, e.g., but not limited to, a 16-bit DAC1009 programmed with the AM DAC command 1006. The power leveling command1007 may drive, e.g., but not limited to, a 6-bit attenuator 1011, whichmay provide compensation for excess gain in microwave amplifiers 1011,1013, at the lower frequencies within a band. The remaining powercontrol element may be, in an exemplary embodiment, the 10 dB stepattenuator command 1008. The 10 dB step attenuator command 1008 maydrive the step attenuator 1014 to discrete states, in 10 dB (Nominal)increments: (0, 10, 20, 30, 40, 50, & 60 dB). The RF output from thestep attenuator 1014 may be routed through a harmonic filter 1015, to aswitch 1016. The switch 1016 may allow the output of SSI 1001 to berouted, e.g., but not limited to, either out to port combiners 1017 orback to a measurement receiver 1018 (described further below withreference to FIG. 3).

FIG. 2 depicts an exemplary embodiment of a diagram 2000 of an exemplaryfunctional overview of the alignment functions. As shown, an EW Testermay be a modular design, including, in an exemplary embodiment, of up to16 output ports 2021 (Port 1 thru Port 16), in which each port may bedriven by up to 8 SSI Assemblies 1001. In smaller systems, allsynthesizers and all ports may not be present, but in the most generalcase, the alignment system must be able to deal with a fully populatedtester (128 SSI Assemblies 1001).

The essential alignment problem is the process of building the Phase Map2028 and Attenuation Map 2029 functions for each SSI Assembly 1001.These functions may include the data conversions that map the run-timecommands 2030 for Phase (Degrees) 2032, Frequency (Hz) 1003, and Power(dBm) 2031 into the hardware controls that cause the correct Phase andPower to be produced at the output port 2021 for each frequency. The mapfunctions in an exemplary embodiment may be implemented as a combinationof alignment data tables (physically stored internal to each SSI 1001),and run-time processing implemented by each SSI 1001.

The essential alignment problem may be complicated by the fact that thehardware elements are continuously drifting, by significant amounts, astemperature changes and other parasitic effects take place. Instead ofbuilding the alignment data tables as a one-time process, the Alignmentfunction must periodically update the data tables, according to anexemplary embodiment. The required update rate may depend on thesensitivity of the specific alignment parameter, and may range from asfast as possible (e.g., less than 1 second) to on-command, according toan exemplary embodiment.

As illustrated in FIG. 2, the output from each SSI 1001 may be switchedoff line 1016 and routed back, through a multiplexing network 2022, to ameasurement receiver 2023. (Only one SSI 1001 at a time may be switchedto the internal measurement path, according to an exemplary embodiment.)The measurement receiver 2023 may be tunable across the full SSIfrequency band (0.5-22 GHz), and may perform quadrature (I, Q) samplingof the measured signal, in an exemplary embodiment.

As illustrated in diagram 3000 of FIG. 3, the measurement receiver 2023,according to an exemplary embodiment, has two separate channels. The “A”Channel is the internal measurement path, capable of cycling through allof the SSIs 1001. The “B” Channel is an external alignment port 2024,with a movable test cable that can be manually connected to the outputof any port.

The Alignment Processing function 2025, according to an exemplaryembodiment, controls the alignment process, switching each SSI 1001 tothe internal measurement path 2022, 2023, sweeping it over frequency,and processing the I, Q data to extract phase and amplitude. Theprocessing function also organizes the alignment data tables and exports(Copies) these data tables to the SSI under alignment, in an exemplaryembodiment.

The Alignment Process, according to an exemplary embodiment, may includeseven separate functions, as follows:

a. Power Leveling

b. Amplifier Compression Characterization

c. Continuous Internal Alignment

d. External Measurement Port Alignment

e. Transfer Alignment of Internal Measurement Paths

f. Time Angle of Arrival Alignment

g. Pulse Width Alignment

Power Leveling 1007, according to an exemplary embodiment, is a processthat measures the Power Leveling Offset (PLO) 1007 required to correctvariations in amplifier gain across the band of frequencies. It is runas part of every power-on sequence, but may also be run on-command(i.e., not while simulations are active). Power leveling is optional,but improves accuracy.

Amplifier Compression Characterization, in an exemplary embodiment, is aprocess that characterizes the phase and amplitude non-linearitiesassociated with compression characteristics of the RF amplifiers 1012,1013. It is run, according to an exemplary embodiment, as part of everypower-on sequence, but may also be run on-command (i.e., not whilesimulations are active).

Continuous Internal Alignment, in an exemplary embodiment, is acontinuously running process in which, every 8 ms, one of the SSIs isswitched off line and routed back to the “A” Channel of the measurementreceiver 2023. As illustrated in diagram 6000 of FIG. 6, during the next8 ms 6057, its phase and amplitude states are measured, in a prioritizedforeground/background processing cycle. The readings are corrected forerrors in the feedback path 2022, so that they accurately reflect phaseand amplitude at the output port 2021. When the measurement sweep iscompleted, the alignment data tables 2028, 2029 are updated to re-alignthe SSI 1001. Then the freshly aligned SSI 1001 is placed back on line,and another may be selected for alignment during the next 8 ms. Theprocess continues, according to an exemplary embodiment, cycling througheach SSI 1001 at a 8 ms rate, thereby aligning every SSI 1001 in thesystem, with an update period of 8 ms per SSI (e.g., 0.768 seconds with96 SSIs 1001 in an exemplary system).

External Measurement Port Alignment, according to an exemplaryembodiment, is a process that aligns the “B” Channel of the measurementreceiver 2024. This operation, according to an exemplary embodiment, isa two-step process. First, as illustrated in FIG. 2, the amplitude termsfor the Internal Measurement Path for SSI_(1,1) are aligned by placing apower meter 2027 on Port 1 2021, then alternately measuring SSI_(1,1)with the external power meter 2027, and again with the “A” Channel ofthe internal measurement receiver 2023. The amplitude correction factorfor the internal path is calculated from the difference in the internaland power meter 2027 readings. Once the amplitude factors for theinternal path are known, according to an exemplary embodiment, the powermeter 2027 may be removed, and the movable test cable from the “B”channel of the measurement receiver may be connected to Port 1. Themeasurement process is repeated, according to an exemplary embodiment,this time comparing the known reading on the “A” channel (with amplitudecorrection applied, so that it accurately reflects power at the Port 1output) with the unknown reading on the “B” channel. The “B” channel isaligned by computing the External Amplitude Correction Factor (EACF) asthe difference between the two readings, according to an exemplaryembodiment.

Transfer Alignment of the Internal Measurement Paths, according to anexemplary embodiment, is a process that computes the Internal AlignmentAmplitude Correction Factors (IAACF) and Internal Alignment PhaseCorrection Factors (IAPCF) values for each measurement path bycorrelating measurements of the output port (i.e., obtained from theexternal measurement port) with measurements from the internal alignmentfeedback paths.

Time Angle of Arrival Alignment, according to an exemplary embodiment,as illustrated in diagram 10000 of FIG. 10, is a process that aligns thetime of arrival of pulse envelope (Pulse Modulator Control). The processconsists of measuring the pulse time of arrival at the output for eachSSI (Via Digital O-Scope 2026), then programming an offset register ineach SSI 1001 to cause the pulses to be aligned in time.

Exemplary Definitions, Nomenclature and Acronyms

Asset Allocation

-   -   Interval: Interval at which available SSI hardware assets are        assigned to specific emitter pulse streams in the EW Simulator.        Nominally 2 ms.

Background

-   -   Cycle: Portion of the 8 ms Frequency Sweep Cycle dedicated to        measurement of lower priority (higher stability) phase and        amplitude parameters.    -   BSA: Base State Amplitude (dBm). This is the Normalized Measured        Amplitude, vs frequency, when the applicable SSI is driven to        the Continuous Internal Alignment Base State (SSI DAC Pwr=SCBSP,        Step Atten=0, SSI Programmed Phase=0). The BSA is a function of        SSI Sub-band (603 values, taken at the center index of each        sub-band).    -   BSP: Base State Phase (Degrees). This is the Normalized Measured        Phase, vs frequency, when the applicable SSI is driven to the        Continuous Internal Alignment Base State (SSI DAC Pwr=SCBSP,        Step Atten=0, SSI Programmed Phase=0). The BSP is a function of        SSI Sub-band (603 values, taken in the center of each sub-band).    -   dBfs: Relative Power, in dB, referenced to Full Scale.    -   dBm: Absolute Power, in dB, referenced to 1 milliwatt.    -   EACF: External Alignment Correction Factor. This value, in units        of dB, must be added to amplitude measurements (dBfs) obtained        from the “B” Channel of the Measurement Receiver. The EACF is a        function of SSI Sub-band (603 values, taken in the center of        each sub-band).    -   FIPC: Filter Induced Phase Contribution (Degrees). This is the        incremental phase shift, within a sub-band, due to distance in        frequency away from the center of the sub-band. The FIPC is a        function of SSI sub-band and frequency, and is measured across        each sub-band in 200 KHz increments.

Foreground

-   -   Cycle: Portion of the 8 ms Frequency Sweep Cycle dedicated to        measurement of high priority (lower stability) phase and        amplitude parameters.

Frequency

-   -   Sweep Cycle: 8 ms time-slice required to measure all foreground        frequency points for a single SSI.    -   HSPD: High-Side Phase Differential. This value, in units of        degrees, is the differential between the phase measurement of        the sub-band center index taken with a high-side LO and the same        measurement made with a low-side LO. It is used for measurement        normalization.    -   IAACFx,y: Internal Alignment Amplitude Correction Factor for        SSIx,y. This value, in units of dB, must be added to amplitude        measurements (dBfs) obtained from the “A” Channel of the        Measurement Receiver for SSIx,y. The IAACF is a function of SSI        Sub-band (603 values, taken in the center of each sub-band).    -   IAPCFx,y: Internal Alignment Phase Correction Factor for SSIx,y.        This value, in units of degrees, must be added to Phase        measurements (Degrees) obtained from the “A” Channel of the        Measurement Receiver for SSIx,y. The IAPCF is a function of SSI        Sub-band and frequency (Up to 190 values per sub-band).    -   PLO: Power Leveling Offset. The attenuator value in dB, as        determined during the Power Leveling process, required to set RF        output power to its optimum value. (603 values, taken in the        center of each sub-band).    -   SAACi: Step Attenuator Amplitude Contribution, in dB, for the        ith 10 dB increment. Six values are measured at the center of        each frequency sub-band, corresponding to −10 dB, −20 dB, −30        dB, −40 dB, −50 dB, and −60 dB, respectively.    -   SAPCi: Step Attenuator Phase Contribution, in degrees, for the        ith 10 dB increment. Six values are measured at the center of        each sub-band, corresponding to −10 dB, −20 dB, −30 dB, −40 dB,        −50 dB, and −60 dB, respectively.    -   SCBSM Saturation-Compensated Base State Magnitude. By        definition, the SCBSM for a particular frequency is a condition        in which the SSI AM DAC is driven at −10 dBfs plus the super        attenuation value (dB) for −10 dBfs (In Range 0), at that        frequency.    -   SCBSΦ Saturation-Compensated Base State Phase. By definition,        the SCBSΦ for a particular frequency is a condition in which the        SSI Phase Control is driven at 0 Degrees minus the SIPC value        (Degrees) for −10 dBfs (In Range 0), at that frequency.    -   SIPC: Saturation Induced Phase Contribution, in degrees. This is        the amount of additional phase shift induced by operating the        SSI AM DAC near its full scale (0 dBfs through −10 sBfs).    -   SSIx,y: Denotes the yth SSI on Port x. For example, SSI_(3,1)        denotes the 1^(st) SSI of Port 3.    -   Super-Attenuation: The amount of additional attenuation (Above        the ideal characteristic) that must be added to compensate the        non-linear effects of amplifier saturation. By convention,        super-attenuation values are referenced to FS power, and are        therefore negative (e.g., −2 dB@−10 dBfs). Super attenuation is        a non-linear characteristic that is small near FS, and increases        to a relatively constant magnitude as attenuation increases        (e.g., −0.2 dB@−1 dBfs, −1 dB@−3 dBfs, −2 dB@−dBfs, −2 dB@−20        dBfs, etc). Super-attenuation is computed from values measured        during Amplifier Compression Characterization. Measurements are        taken at the center of each frequency sub-band, in three ranges,        corresponding to the −10 dB, −20 dB, and −30 dB through −60 dB        states of the step attenuator.        Measurement Process

Measurement Receiver

The Measurement Receiver is functionally illustrated in FIG. 3,according to an exemplary embodiment. Each of the up to 128 SSIs 1001may be routed through the summing multiplexer 2022, one at a time, to bemeasured on the “A” Channel A/D Converter 3042. The “B” Channel A/DConverter 3047 may provide a parallel measurement of the ExternalAlignment Port 2024. An additional SSI 3040 may serve as a tunable localoscillator (SSI LO), common to both channels, according to an exemplaryembodiment, and may be offset from the SSI 1001 being measured by 6.25MHz, to produce a 6.25 MHz IF at the A/D Converters 3042, 3047.

The A/D Converters 3042,3047, according to an exemplary embodiment, usecoherent matched-filter sampling to take I & Q data samples of the 6.25MHz IF. The sampling rate is 25 MHz, according to an exemplaryembodiment, which is four times the 6.25 MHz IF 3043, 3044, 3045. Thesamples are processed, in a matched filter scheme, to extract I & Qvalues, in an exemplary embodiment.

The SSI architecture, according to an exemplary embodiment, isinternally divided into 37 MHz (Nominal) sub-bands. In order to maximizestability, the SSI LO 3040 must be kept within the same sub-band as theSSI 1001 under test. This may be done, according to an exemplaryembodiment, as follows:

a) When the SSI 1001 under test is in the upper half of the sub-band,the SSI LO 3040 is set 6.25 MHz below the measurement frequency(Low-side measurement), according to an exemplary embodiment.

b) When the SSI 1001 under test is in the lower half of the sub-band,the SSI LO 3040 is set 6.25 MHz above the measurement frequency(High-side measurement), according to an exemplary embodiment.

c) The sub-band center frequency is measured twice, according to anexemplary embodiment; once as a low-side measurement, and again as ahigh-side measurement. The low-side measurement is used as the phase andamplitude reference for the sub-band. The difference between thehigh-side and low-side measurements of the center frequency is used tocompute phase and amplitude correction factors (high-side phasecorrection (HSPD) and high-side amplitude correction (HSAD)) to apply toall high-side measurements in that sub-band.

Basic Measurement Cycles

The Alignment process, according to an exemplary embodiment, uses abasic measurement cycle (Single measurement of phase and amplitude), asillustrated in diagram 4000 of FIG. 4. This basic cycle, according to anexemplary embodiment, is actually a compound measurement, usingdifferential processing to cancel voltage standing wave ratio (VSWR)interference effects. For further information about VSWR cancellation,see U.S. patent application Ser. No. 11/369,986, entitled “Method andSystem for Eliminating VSWR Errors in Magnitude Measurements,” and seeU.S. patent application Ser. No. 11/369,997, entitled “Method and Systemfor Eliminating VSWR Errors in Phase and Amplitude Measurements,” ofcommon assignee to the present invention, the contents of which isincorporated herein by reference in its entirety. It consists ofback-to-back elementary measurements, taken with the signal phase offsetby 180° between the two.

Two measurement cycle timelines are shown, according to an exemplaryembodiment: Fast 4050 and Extended 4051. The only difference between thetimelines is the number of microseconds, N, over which the elementarymeasurements are integrated. The fast cycle (N=1; 4 μs total duration)is used with strong signals, and gives the quickest measurementresponse, according to an exemplary embodiment. The extended cycle (N>1;2N+2 μs total duration) is a parametric extension of the cycle thatallows for longer measurement dwell in cases of low signal to noiseratio (SNR), according to an exemplary embodiment. Regardless of thelength of the measurement dwell (N), all timelines allow a 1-microsecondsettling time for the SSI signal to transition and settle tosteady-state before the A/D samples are collected.

For each of the two elementary measurements made during a measurementcycle, the A/D samples are processed to produce an estimate of theIn-Phase (I) and Quadrature-Phase (Q) components of the measured signal.The processing to extract I and Q values from the A/D samples (Si) is asfollows:

$I = {{\left( {{1/12}N} \right){\sum\limits_{i = 0}^{{6N} - 1}S_{4i}}} - S_{{4i} + 2}}$$Q = {{\left( {{1/12}N} \right){\sum\limits_{i = 0}^{{6N} - 1}S_{{4i} + 1}}} - S_{{4i} + 3}}$

For example, in the special case of the Fast Cycle (N=1), the elementaryI and Q values are computed from the following equations, according toan exemplary embodiment:I= 1/12[(S0−S2)+(S4−S6)+(S8−S10)+(S12−S14)+(S16−S18)+(S20−S22)]Q= 1/12[(S1−S3)+(S5−S7)+(S9−S11)+(S13−S15)+(S17−S19)+(S21−S23)]

The I and Q detection processing detailed above, according to anexemplary embodiment, is a matched filter to the 6.25 MHz IF waveform.Effective Bandwidth is approximately 1 MHz for the Fast Cycle. TheDetection Transfer Function (DTF) for the fast cycle is shown, accordingto an exemplary embodiment, in chart 5000 of FIG. 5. The extended cycleDTF has the same shape, but the pass-band becomes narrower as theintegration time is extended.

Computing Measured Amplitude & Phase

The compound measurement process illustrated in FIG. 4 cancels voltagestanding wave ratio (VSWR) interference by making two elementarymeasurements, inverting the signal phase between them, and usingdifferential processing to compute the composite result. This process,according to an exemplary embodiment, may include the following steps:

The first elementary measurement is made, according to an exemplaryembodiment, with the signal under test set to its reference phase (0°offset). The A/D data is processed, per the Basic Measurement Cycles ofFIG. 4 discussed above, to compute a first estimate of the I & Qcomponents of the signal under test (I₁ & Q₁).

The second elementary measurement is made with the signal under testinverted in phase (180° offset). The A/D data is processed, per BasicMeasurement Cycles of FIG. 4 discussed above, to compute a secondestimate of the I & Q components of the signal under test (I₂ & Q₂).

A true reading for the signal I & Q components is computed as follows:I=(I ₁ −I ₂)/2 Q=(Q ₁ −Q ₂)/2

The true Amplitude and true Phase of the signal under test is computedfrom the true readings of the I & Q components, in accordance with thefollowing relations:Amplitude(dBfs)=20 Log [(Sqrt[I ² +Q ² ]/ADCfs)]Phase(Deg)=(180/Pi)ArcTan [Q/I]

Where: 1. ADCfs is the full scale reading of the A/D

-   -   2. “ArcTan” is a 4-quadrant Arc Tangent function

Measurement Normalization

Each measurement that is taken must be Normalized, according to anexemplary embodiment, in phase and amplitude, so that it accuratelyrepresents phase and amplitude at the applicable output port. Thisprocess involves several steps, as follows, according to an exemplaryembodiment:

a. Compute Measured Amplitude (dBfs) and Measured Phase (Deg) perSection Basic Measurement Cycles, & Computing Measured Amplitude &Phase, above;

b. If applicable, compensate Measured Amplitude and Phase for High-SideLO;

c. Add the appropriate IAACF (dB) to the Compensated Measured Amplitude(dBfs) to compute the Normalized Measured Amplitude (dBm); and/or

d. Add the IAPCF (Degrees) to the Compensated Measured Phase (Degrees)to Compute the Normalized Measured Phase.

Measurements may be made with either a high-side or low-side LO, per theMeasurement Receiver 2023 (discussed with reference to FIGS. 2 and 3)above. If the LO is on the low side, the Compensated Measured Phase(CMP) is simply the measured phase, and the Compensated MeasuredAmplitude (CMA) is simply the measured amplitude. If, however, the LO ison the high side, the CMP is the measured phase plus the High Side PhaseDifferential (HSPD), and the CMA is the measured amplitude plus the HighSide Amplitude Differential:

-   -   If[LO=Low Side] then:

CMP=Measured Phase;

CMA=Measured Amplitude;

-   -   ELSE:

CMP=Measured Phase+HSPD;

CMA=Measured Amplitude+HSAD;

Each SSI 1001 has an associated IAACF and IAPCF data table (Amplitudeand Phase vs Frequency). IAACF data is stored for the center of eachsub-band, and is valid for all frequencies in the sub-band. IAPCF isstored in 200 KHz increments, so there is one IAPCF value stored foreach frequency used for internal alignment. Normalized measurements areproduced by simply adding the specific correction factors to thecompensated measured data.

Note: Measurements taken on the “B” Channel must also be normalized asnoted above. However, EACF is used in place IAACF in step c, and step dis omitted (No phase correction, other than for LO side, is made on theexternal channel).

Power Leveling

Power Leveling 1007, according to an exemplary embodiment, serves tocorrect variations in amplifier gain and compression across the band offrequencies. This correction is applied, according to an exemplaryembodiment, in a separate 6-bit digital attenuator 1011, so as not toconsume dynamic range in the SSI AM DAC 1009.

Power Leveling 1007, according to an exemplary embodiment, may includeadjusting the full scale power out-put of each SSI 1001 so that it isapproximately +2 dBm, or is saturated, which ever is less (i.e., +2 dBprovides head-room for Continuous Internal Alignment to make adjustmentsas gains change with temperature, but channels will not have reservepower at the upper band edges, and will likely saturate before the +2 dBreserve level is met).

Power Leveling 1007, according to an exemplary embodiment, is run aspart of every power-on sequence, but may also be run on-command (Notwhile simulations are active). The output of Power Leveling 1007 is atable of values for the 6-Bit digital attenuator 1011 as a function offrequency (Part of the ATTEN MAP function 2029 illustrated in diagram8000 of FIG. 8, and described further in reference thereof). Atrun-time, the appropriate value must be retrieved from the table andloaded into the 6-Bit Leveling Attenuator whenever the frequency isupdated, according to an exemplary embodiment. This update must besynchronized with the update of other attenuators, according to anexemplary embodiment, so as to prevent glitching.

It is important to note that the Microwave amplifiers can exhibiterratic behavior when they are in hard saturation, according to anexemplary embodiment. For this reason, the digital attenuator must bedriven with enough bits to ensure that the amplifiers are not saturated,then attenuation gradually removed until the amplifiers reach thedesired output power, or begin to saturate, in an exemplary embodiment.The process is summarized as follows, according to an exemplaryembodiment:

a. Select the SSI 1001 to be leveled and route its output to theMeasurement Receiver 2023;

b. Apply half scale (16 dB) to the Digital Attenuator;

c. Set the SSI frequency to the center of the first sub-band;

d. Wait 1 ms to ensure amplifiers have time to exit saturation;

e. Measure Amplitude from the Measurement Receiver 2023 (Fast Cycle);

f. Decrement Digital Attenuator Code (+0.5 dB nominal step);

g. Measure Amplitude from the Measurement Receiver 2023 (Fast Cycle);and/or

h. Compute the dB change of most recent measurement with respect to theprevious measurement.

If the change is greater than a threshold (Default=0.1 dB), and theoutput power is less than +2 dBm, according to an exemplary embodiment,decrement the digital attenuator code & repeat steps g & h. Else, storethe attenuator value as the Power Leveling Offset (PLO) for thatsub-band, and move the SSI frequency to the center of the next sub-band.

The process is repeated, according to an exemplary embodiment, for eachSSI sub-band between 0.5 MHz and 22 GHz (603 pts), with frequency set tothe center of the sub-band. Approximate time to build the table ofvalues is 0.7 seconds per SSI 1001, or 96 SSIs in 70 seconds, accordingto an exemplary embodiment.

Amplifier Compression Alignment

A purpose of the Amplifier Compression Alignment, according to anexemplary embodiment, is to characterize the non-linearity (CompressionResponse) of the composite chain of microwave amplifiers (12, 13)between the SSI digital source 1002 and the Port Output 1005. Becausethe amplifiers and attenuation controls are distributed throughout thechain, there are potential non-linear effects associated with both theSSI AM DAC 1009 and the Step Attenuators 1014. This issue is addressedby characterizing the compression response in three ranges, as follows,according to an exemplary embodiment:

Range 0: Step Attenuator = 0 dB Range 1: Step Attenuator = −10 dB Range2: Step Attenuator = −20 dB

TABLE 1 Measurement Parameters for Amplifier Compression Alignment MEASMEASUREMENT ACCURACY APPROX INTEGRATION MEAS CYCLE RANGE(Atten_(Desired)) THRESHOLD SNR @ A/D TIME “N” TIME 0     0 dB ReferenceN/A 65 1 μs 4 μs −0.25 dB ±0.05 dB 65 1 μs 4 μs  −0.5 dB ±0.05 dB 65 1μs 4 μs  −1.0 dB  ±0.1 dB 64 1 μs 4 μs  −2.0 dB  ±0.1 dB 63 1 μs 4 μs −4.0 dB  ±0.2 dB 61 1 μs 4 μs  −8.0 dB  ±0.2 dB 57 1 μs 4 μs −16.0 dB ±0.2 dB 49 1 μs 4 μs 1     0 dB Reference N/A 65 1 μs 4 μs −0.25 dB±0.05 dB 55 1 μs 4 μs  −0.5 dB ±0.05 dB 55 1 μs 4 μs  −1.0 dB  ±0.1 dB54 1 μs 4 μs  −2.0 dB  ±0.1 dB 53 1 μs 4 μs  −4.0 dB  ±0.2 dB 51 1 μs 4μs  −8.0 dB  ±0.2 dB 47 1 μs 4 μs −16.0 dB  ±0.2 dB 39 2 μs 6 μs 2     0dB Reference N/A 65 1 μs 4 μs −0.25 dB ±0.05 dB 45 1 μs 4 μs  −0.5 dB±0.05 dB 45 1 μs 4 μs  −1.0 dB  ±0.1 dB 44 1 μs 4 μs  −2.0 dB  ±0.1 dB43 1 μs 4 μs  −4.0 dB  ±0.2 dB 41 1 μs 4 μs  −8.0 dB  ±0.2 dB 37 2 μs 6μs −16.0 dB  ±0.2 dB 29 12 μs  26 μs  Total Measurement Time (1Iteration): 124 μs 

The data from Range 2 is valid for all Step Attenuator states beyond −20dB (i.e., −30, −40, −50, −60), according to an exemplary embodiment.This is due to the fact that nonlinear effects associated with the StepAttenuator 1014 become insignificant once it is down 20 dB, and the onlynonlinear effect remaining is associated with the SSI AM DAC 1009, whichis common for all higher attenuation states.

In each range, phase and amplitude measurements are made at thefollowing discrete attenuation states (dB): −0.25, −0.5, −1.0, −2.0,−4.0, −8.0, −16.0 (Attenuation additional to the Step Atten). Theseseven data points characterize the saturation phenomena, according to anexemplary embodiment. At run-time, the SSI 1001 computes the exact valuefor Super-Attenuation and SIPC by completing a quadratic interpolationof Super-Attenuation and SIPC values measured at these data points,according to an exemplary embodiment.

The process operates by driving the SSI AM DAC 1009 to whatever value isrequired to produce the desired attenuation, within a specifiedtolerance, then recording the phase and super-attenuation measurementsfor that attenuation state, according to an exemplary embodiment. Themeasurement parameters for all measurements required for AmplifierCompression Alignment are shown in Table 1, for an exemplary embodiment.

The measurements use a search algorithm that begins with the nominalvalue for desired attenuation, measures the actual attenuation, andcorrects the initial estimate by the differential (in dB), according toan exemplary embodiment. A maximum of three iterations (On Average) arerequired to converge on each attenuation point, according to anexemplary embodiment. Total time for Amplifier Compression Alignment istherefore estimated as follows, according to an exemplary embodiment:124 μs/Iteration/sub-band×3 Iterations×603 sub-bands=0.224 seconds perSSI

Thus, estimated time required for Amplifier Compression Alignment forthe PLAID Configuration (96 SSIs) is 21.5 seconds, according to anexemplary embodiment.

Amplifier Compression Measurement Process

Amplifier Compression Alignment, according to an exemplary embodiment,is run in each SSI sub-band, with frequency set to the center of thesub-band. Since both Super-Attenuation and SIPC are relatively stableacross a sub-band, the measured data produces composite values for useanywhere within the sub-band, in an exemplary embodiment.

The process for measuring the Amplifier Compression Characteristics issummarized as follows, according to an exemplary embodiment:

a. Select the SSI to be characterized and route its output to theMeasurement Receiver;

b. Set the SSI frequency to the center of the sub-band;

c. Apply the Power Leveling correction data for that frequency;

d. Set the appropriate Step Attenuator State for the Range to bemeasured;

e. Drive the SSI AM DAC to Full Scale (0 dBfs);

f. Measure Reference Amplitude (Amp_(Ref); dBfs);

g. Drive the SSI AM DAC to achieved desired attenuation(Atten_(Desired)), per the search algorithm detailed below;

h. Compute Super-Attenuation: Super-Atten=AM DAC Control−Atten_(Act);

i. Record Super-Attenuation (dB) and Phase (Deg) vs attenuation datapoint;

j. Repeat Steps e and f for each attenuation data point (7, per Table1);

k. Compute SIPC from measured phase values by subtracting the phasevalue measured at the −16 dB attenuation data point from each phasemeasurement:SIPC_(n)=Phase_(Meas,n)−Phase_(Meas, −16 dB);

l. Repeat Steps d through k for each Range (3, per Table 1); and/or

m. Repeat Steps b through l for each sub-band (603, per Appendix C).

Note: SIPC is defined as the incremental phase shift (e.g., delta phase)induced as the amplifier is driven into saturation, according to anexemplary embodiment. This implies that the SIPC at high levels ofattenuation is zero (By definition). The −16 dB attenuation data pointtherefore becomes the phase reference for SIPC, as no saturation-inducedeffect is expected below this level, in an exemplary embodiment (Thephase shift associated with each step attenuator state is determined bythe Continuous Alignment Process, and is not part of SIPC).

Search Algorithm

Because the compression characteristics cause the Command-to-Actualattenuation transfer function to be nonlinear, the command required toachieve the desired level of attenuation will differ from its nominalvalue, according to an exemplary embodiment. It is necessary, therefore,to iteratively drive the SSI AM DAC to converge on the correct value ofattenuation, in an exemplary embodiment. The purpose of the followingalgorithm is to converge as rapidly as possible, according to anexemplary embodiment:

a. Start with AM DAC Control=Atten_(Desired) (dBfs);

b. Measure Amplitude (Amp_(Meas); dBfs), and Phase (Phase_(Meas); Deg),using integration time specified in Table 1;

c. Compute Attenuation: Atten_(Act)=Amp_(Meas)−Amp_(Ref);

d. Error (dBfs)=Atten_(Desired)−Atten_(Act);

e. If Abs[Error]<Threshold, Stop; Return AM DAC Control, Atten_(Act),and Phase_(Meas),

f. Iterate Control: AM DAC Control_(n+1)=AM DAC Control_(n)+Error;and/or g. Repeat steps c thru e until d is true.

Amplifier Compression Data Reduction & Export

The measurement process described above, according to an exemplaryembodiment, results in Data Tables for Super-Atten & SIPC (7 values perrange, 3 ranges, 603 sub-bands). This must be exported to the SSI 1001under alignment for use at run-time.

This data is interpolated at run-time, internal to the SSI 1001, usingpiece-wise quadratic interpolation. Since the piece-wise interpolationoperates between 3 ordered pairs, the 7 attenuation data points aregrouped as shown in Table 2, each group being valid over the specifiedrange of interpolation, according to an exemplary embodiment.

TABLE 2 Data Groupings for Piece-wise Quadratic Interpolation RANGE OFINTERPOLATION (AM DAC GROUP PWR, per FIG. 3.1-3) DATA PAIR x f(x) 0   0to −1.0 dB {x₀, f₀} −0.25 dB  f(−0.25 dB)  {x₁, f₁}  −.5 dB f(−0.5 dB){x₂, f₂} −1.0 dB f(−1.0 dB) 1 −1.0 to −4.0 dB {x₀, f₀} −1.0 dB f(−1.0dB) {x₁, f₁} −2.0 dB f(−2.0 dB) {x₂, f₂} −4.0 dB f(−4.0 dB) 2 −4.0 to−16.0 dB  {x₀, f₀} −4.0 dB f(−4.0 dB) {x₁, f₁} −8.0 dB f(−8.0 dB) {x₂,f₂} −16.0 dB  f(−16.0 dB) 

Continuous Internal Alignment Process

Note: Power Leveling and Amplifier Compression Alignment must be runprior to activating the Continuous Internal Alignment process, and thePLO correction factors developed in Power Leveling must be applied tothe 6-bit attenuator as the Continuous Internal Alignment process runs,according to an exemplary embodiment. The amplitude and phasecontributions of the Power Leveling function are captured in the basestate measurements, in an exemplary embodiment.

There are three aspects to the Continuous Internal Alignment function,as follows, according to an exemplary embodiment:

a. Frequency Sweep Cycle (see diagram 6000 of FIG. 6);

b. Data Export to the SSI 1001; and/or

c. Run-time Data Application in the SSI 1001.

Frequency Sweep Cycle

The Continuous Internal Alignment process, according to an exemplaryembodiment, is run in 8 ms time slices 6057, as illustrated in diagram6000 of FIG. 6. Each SSI 1001 is switched to the internal measurementpath for alignment, on a rotating basis, for one 8 ms time slice, orFrequency Sweep Cycle 6053, according to an exemplary embodiment. These8 ms time slices are synchronous with the 2 ms Asset AllocationInterval, so switching an SSI to the measurement receiver does notdisrupt emitter pulse trains in the EW simulator, according to anexemplary embodiment.

The foreground cycle 6054 measures the base-state phase and amplitude atthe center of each sub-band, according to an exemplary embodiment.Measurements are made using the Fast Cycle 4050. At 4 microseconds permeasurement, 2.412 ms are required to complete the sweep of all 603sub-bands. These are the high priority measurements, designed tostabilize thermally induced phase drift. All foreground measurements arecompleted in a single 8 ms time-slice, with the result that foregroundmeasurements are updated each alignment cycle (i.e., every 0.768 secondswith 96 SSIs present).

The background cycle 6055, according to an exemplary embodiment,conducts more detailed measurements at a slower update rate. These arethe lower priority measurements of quasi-static parameters (e.g.,parameters that have much lower thermal sensitivity). The backgroundprocess completely characterizes 5 of the 603 sub-bands during an 8 mstime-slice, rotating the group of 5 with each pass through the alignmentcycle, so that all 603 sub-bands have been measured after 121 passesthrough the alignment cycle. (Update Rate with 96 SSIspresent=121×0.768=93 seconds.) Background measurements include adetailed mapping of filter-induced phase pull (200 KHz increments, or188 measurements across each sub-band), as well as the phase andamplitude characteristics of each of six step-attenuator states (Centerfrequency of each sub-band, times 6 attenuator states), according to anexemplary embodiment. The measurement timing for background measurementsis specified in Table 3, according to an exemplary embodiment.

TABLE 3 Timing for Background Measurements NUMBER OF EXTENDEDMEASUREMENTS APPROX INTEGR MEAS TIME PER PARAMETER PER SUB-BAND SNR @A/D TIME (N) TIME SUB-BAND HSPD/HSAD 1 55 1 μs 4 μs 4 μs FIPC 188 (Ave)55 1 μs 4 μs 752 μs  SAPC/SAAC 1 65 1 μs 4 μs 4 μs Reference (0 dB)SAPC/SAAC (−10 dB) 1 55 1 μs 4 μs 4 μs SAPC/SAAC (−20 dB) 1 45 1 μs 4 μs4 μs SAPC/SAAC (−30 dB) 1 35 1 μs 4 μs 4 μs SAPC/SAAC (−40 dB) 1 25 3 μs8 μs 8 μs SAPC/SAAC (−50 dB) 1 15 16 μs  34 μs  34 μs  SAPC/SAAC (−60dB) 1 5 72 μs  146 μs  146 μs  Total Background Measurement Time (1Sub-band): 960 μs 

The rate at which individual SSIs 1001 are aligned is dependent on howmany SSIs are in the system. SSIs 1001 are rotated on a 8 ms basis(e.g., one Frequency Sweep Cycle 6053 per SSI 1001), and sequencecontinuously through each SSI 1001 in the system. The resultingalignment rates for typical configurations are summarized in Table 4,according to an exemplary embodiment.

TABLE 4 Alignment Update Rates as a Function of Installed SSIs SWEEPALIGNMENT REFRESH RATE CONFIGURATION # OF SSIs CYCLE FOREGROUNDBACKGROUND Maximum: 16 Port × 8 Deep 128 8 mS 1.024 Sec 123.9 Sec Large: 16 Port × 6 Deep 96 8 mS 0.768 Sec 92.9 Sec Moderate: 8 Port × 7Deep 56 8 mS 0.448 Sec 54.2 Sec Small: 4 Port × 4 Deep 16 8 mS 0.128 Sec15.5 Sec Minimal: 2 Port × 2 Deep 4 8 mS 0.032 Sec 3.87 Sec

Foreground Measurements

The foreground Frequency Sweep 6054, as described below, is conducted atpower levels approximately 10 dB below full scale (SSI AM DACMagnitude=SCBSM; Step Atten=0 dB, Programmed Phase=SCBSP), according toan exemplary embodiment. This is the Internal Alignment Base State, andis approximately 10 dB below full scale to ensure that the non-lineareffects of power amplifier saturation are not a contaminating influenceto the alignment, according to an exemplary embodiment.

Base-State Phase and Amplitude

The Base State Phase (BSP) and Base State Amplitude (BSA), according toan exemplary embodiment, are measured at the center of each sub-band(See diagram 7000 of FIG. 7). Both parameters are computed from a singlefast-cycle measurement, according to an exemplary embodiment. Allmeasurements are made with the SSI driven to the Internal Alignment BaseState (SSI AM DAC Magnitude=SCBSM; Step Atten=0 dB, ProgrammedPhase=SCBSΦ), according to an exemplary embodiment. BSA data is theNormalized Measured Amplitude (dBm). BSP data is the Normalized MeasuredPhase (Degrees), according to an exemplary embodiment.

Background Measurements

High-Side Phase and Amplitude Differentials

The High-Side Differentials are measured at the center of each sub-band(See diagram 7000 of FIG. 7), at exactly the same point and at exactlythe same drive level (e.g., SSI driven to the Internal Alignment BaseState) as is used for the foreground (BSA/BSP) measurements, accordingto an exemplary embodiment. The only difference is that a High-Side LOis used for measuring the differentials, according to an exemplaryembodiment.

The High-Side Differentials for phase and amplitude, (HSPD) and (HSAD),respectively, are defined as follows:HSPD=BSP−Partially Normalized Measured PhaseHSAD=BSA−Partially Normalized Measured Amplitude

In this context, partial normalization denotes that the path-losscorrections described in Measurement Normalization, above, are applied,but correction for High-Side LO is not, according to an exemplaryembodiment.

Filter-Induced Phase Contribution

FIPC Measurement

Filter Induced Phase Contribution, according to an exemplary embodiment,is measured across a sub-band, in 200 KHz increments. All FIPCmeasurements are made at the Internal Alignment Base State (SSI AM DACMagnitude=SCBSM; Step Atten=0 dB, Programmed Phase=SCBSΦ), according toan exemplary embodiment. Measurements are made on either side of thesub-band center frequency, in e.g., but not limited to, 200 KHzincrements, according to an exemplary embodiment.

Note: The center frequency is not measured as part of FIPC, according toan exemplary embodiment. Per the discussion above with reference to themeasurement receiver 2023 and FIG. 3, all measurements in the upper halfof the sub-band are made with a Low-Side LO, while all measurements inthe lower half are made with a High-Side LO. The HSPD/HSAD correctionfactors apply to all high-side measurements, per MeasurementNormalization, above, according to an exemplary embodiment.

The arrangement of FIPC measurements within a sub-band is illustrated indiagram 7000 for case 1 7002 and case 2 7004 of FIG. 7. As shown, anIndex system is used to represent the number of exemplary 200 KHzincrements from the lower frequency edge of the band, according to anexemplary embodiment. The Indexing system simplifies frequencyreferencing and minimizes data storage requirements, according to anexemplary embodiment. FIG. 7 is a simplified exemplary schematic. Thereare many more index points across the sub-band, and the max index(Max_i) is typically either 185 or 190, according to an exemplaryembodiment.

The concept for correcting for FIPC is to sample Phase on a dense gridacross frequency, then, during system run-time, use piece-wise quadraticinterpolation to compute the precise FIPC correction, according to anexemplary embodiment. FIG. 7 also illustrates the set groupings for thepiece-wise interpolation, according to an exemplary embodiment.

Because the sub-bands vary in width, the number of index points acrossthe band is also a variable, in an exemplary embodiment. If the maximumindex is Even (Case 1 in FIG. 7), the Sub-band center is the actualfrequency mid-point, and the groupings are even and symmetrical. Thefollowing relationships apply, according to an exemplary embodiment:Lower Edge=0 Upper Edge=Max_(—) i Center=Max_(—) i/2Number of Interpolation Groups=Max_(—) i/2Interpolation Group=Floor[i/2]; for 0≦i<Max_(—) i

If the maximum index is Odd (Case 2 in FIG. 7) the Sub-band center isthe nearest index below the actual frequency mid-point, and thegroupings are asymmetrical, in an exemplary embodiment. An extra groupis required to interpolate the last 200 KHz, according to an exemplaryembodiment. The following relationships apply, according to an exemplaryembodiment:

Lower  Edge = 0 Upper  Edge = Max_I Center = (Max_i/2) − 0.5Number  of  Interpolation  Groups = 1 + Floor[Max_i/2] $\begin{matrix}{{{{Interpolation}\mspace{14mu}{Group}} = {{Floor}\left\lbrack {i/2} \right\rbrack}};{{{for}\mspace{14mu} 0} \leq i < {{Max\_ i} - 1}}} \\{{= {{Floor}\left\lbrack {{Max\_ i}/2} \right\rbrack}};{{{{for}\mspace{14mu}{Max\_ i}} - 1} \leq i < {Max\_ i}}}\end{matrix}$

FIPC Data Reduction & Export

The measurement process described above results in Data Tables for FIPC(200 KHz increments, arranged by Index, Approx 188 (Ave) per sub-band,603 sub-bands), according to an exemplary embodiment. This must beexported to the SSI 1001 under alignment for use at run-time, accordingto an exemplary embodiment.

This data is interpolated at run-time, internal to the SSI 1001, usingpiece-wise quadratic interpolation. Since the piece-wise interpolationoperates between 3 ordered pairs, the FIPC data points are grouped asshown in Table 5, each group being valid over the specified range ofinterpolation, according to an exemplary embodiment.

TABLE 5 Data Groupings for Piece-wise Quadratic Interpolation of FIPCRANGE OF INTERPOLATION DATA GROUP (Intra-band Frequency Index) PAIR xf(x) 0 0 to 2 {x₀, f₀} 0 FIPC(0) {x₁, f₁} 1 FIPC(1) {x₂, f₂} 2 FIPC(2) 12 to 4 {x₀, f₀} 2 FIPC(2) {x₁, f₁} 3 FIPC(3) {x₂, f₂} 4 FIPC(4) . . . N2N to 2N + 2 {x₀, f₀} 2N f(2N) (Case 1: Max_i is Even) {x₁, f₁} 2N + 1f(2N + 1) {x₂, f₂} 2N + 2 f(2N + 2) N − 1 2N − 2 to 2N {x₀, f₀} 2N − 2f(2N − 2) (Case 2: Max_i is Odd) {x₁, f₁} 2N − 1 f(2N − 1) {x₂, f₂} 2Nf(2N) N 2N − 1 to 2N + 1 {x₀, f₀} 2N − 1 f(2N − 1) (Case 2: Max_i isOdd) {x₁, f₁} 2N f(2N) {x₂, f₂} 2N + 1 f(2N + 1)

Step Attenuator Contributions

The step attenuator 1014 contributions (Amplitude and Phase, vsfrequency), according to an exemplary embodiment, are measured duringthe background cycle of the Continuous Internal Alignment process. Thisprocess, according to an exemplary embodiment, produces a series of 6values for SAAC (Amplitude) and SAPC (Phase), corresponding to the sixattenuation states (10, 20, 30, 40, 50, & 60 dB).

Because the measurements of SAAC and SAPC contain relatively high noise(Particularly at high attenuation states), and these parameters aregenerally very stable (˜100 ppm/° C.), the actual value of SAAC and SAPCwill be taken as the output of a state-variable estimator, as notedbelow, according to an exemplary embodiment.

Parameter Measurements

The values for SAAC and SAPC are computed as differentials from afull-power Reference Measurement (Amplitude and Phase), according to anexemplary embodiment. All Measurements are to be made with the SSI AMset to full scale, according to an exemplary embodiment. For eachsub-band, SAAC and SAPC values are computed as follows, according to anexemplary embodiment:SAAC Ref=Normalized Measured Amplitude(Step Atten=0 dB)SAAC₀=0(By definition)SAAC₁(Meas)=Normalized Measured Amplitude(Step Atten=−10 dB)−SAAC RefSAAC₂(Meas)=Normalized Measured Amplitude(Step Atten=−20 dB)−SAAC RefSAAC₃(Meas)=Normalized Measured Amplitude(Step Atten=−30 dB)−SAAC RefSAAC₄(Meas)=Normalized Measured Amplitude(Step Atten=−40 dB)−SAAC RefSAAC₅(Meas)=Normalized Measured Amplitude(Step Atten=−50 dB)−SAAC RefSAAC₆(Meas)=Normalized Measured Amplitude(Step Atten=−60 dB)−SAAC RefSAPC Ref=Normalized Measured Phase(Step Atten=0 dB)SAPC₀=0(By definition)SAPC₁(Meas)=Normalized Measured Phase(Step Atten=−10 dB)−SAPC RefSAPC₂(Meas)=Normalized Measured Phase(Step Atten=−20 dB)−SAPC RefSAPC₃(Meas)=Normalized Measured Phase(Step Atten=−30 dB)−SAPC RefSAPC₄(Meas)=Normalized Measured Phase(Step Atten=−40 dB)−SAPC RefSAPC₅(Meas)=Normalized Measured Phase(Step Atten=−50 dB)−SAPC RefSAPC₆(Meas)=Normalized Measured Phase(Step Atten=−60 dB)−SAPC Ref

The values for both SAAC and SAPC have a low dependence on frequency,according to an exemplary embodiment. The values may be measured in thecenter of the sub-band to get a composite value for use within thesub-band, according to an exemplary embodiment.

State Variable Estimation

The exact values for SAAC and SAPC are typically much more stable thanindividual measurements of these parameters. The exact values willtherefore be calculated as the output of a state estimation filter,according to an exemplary embodiment. The form of the filter is the samefor both SAAC and SAPC values, as follows, according to an exemplaryembodiment:

Start-Up Sequence:Est(0)=Meas(0)(*Filter is initialized with 1^(St) Measurement*)Est(1)=[Meas(0)+Meas(1)]/2Est(2)=[Meas(0)+Meas(1)+Meas(2)]/3Est(3)=[Meas(0)+Meas(1)+Meas(2)+Meas(3)]/4Est(4)=[Meas(0)+Meas(1)+Meas(2)+Meas(3)+Meas(4)]/5

Steady-State Sequence:Est(n)=Est(n−1)+k*(Meas(n)−Est(n−1))

The parameter k defines the integration time, and may be different foreach attenuation state (Optimum performance occurs when k is tailored tothe expected measurement SNR), according to an exemplary embodiment.Simulation results indicate that k=0.1 gives reasonable performance at 5dB SNR (Expected worst-case noise condition for measuring=60 dB stepattenuator state), according to an exemplary embodiment.

Data Export to SSI

As the Continuous Internal Alignment Frequency Sweep Cycle is run, datamust be exported to the SSI under alignment, according to an exemplaryembodiment. Data transfer requirements are summarized as follows,according to an exemplary embodiment:

Data Transfer During Continuous Alignment

a. Foreground Data (Each 8 ms sweep)

BSA: 302 Words BSP: 302 Words

b. Background Data (Each 8 ms sweep; 5 out of 603 sub-bands)

FIPC: 470 Words (188 meas per sub-band (Ave)/2 meas per word) FIPCInterp Coeffs: 470 Words SAAC:  20 Words (4 Words per Sub-band) SAPC: 20 Words (4 Words per Sub-band)

Data Transfer at Other Times (Reference)

c. Power Leveling (Once at Power-up & On command)

PLO: 302 Words

d. Amplifier Compression Sweep (Once at Power-up & On command)

Super-Atten: 7,236 Words SA Interp Coeffs: 5,427 Words SIPC: 7,236 WordsSIPC Interp Coeffs: 5,427 Words

e. Pulse Alignment (On command; Requires external instrumentation)

PMOD Delay Map: 512 Words PMOD Insert Delay:  1 Word

Data transfer must be complete by the end of the 8 ms Frequency SweepCycle 6053 so that the SSI has all required data when it is placed backon line, according to an exemplary embodiment. The purpose of allocatingthe spare 0.778 ms at the end of the cycle is to facilitate the requireddata transfer, according to an exemplary embodiment.

Run-Time Data Application in SSI

The following functions must be executed internal to the SSI 1001 atrun-time, according to an exemplary embodiment. These functions are partof the alignment subsystem, but are allocated to the SSI 1001, insteadof to the Alignment Processing Function 2025, according to an exemplaryembodiment.

Building the Attenuation Map

General

The process for constructing the Attenuation Map 2029, according to anexemplary embodiment, is illustrated in diagram 8000 of FIG. 8. Asshown, the Attenuation Map 8060, according to an exemplary embodiment,may include a level shift 8060, a parsing of the required relative powerbetween the step attenuator and the SSI AM DAC 8062, the addition ofsuper attenuation 8063, and a theoretical conversion 8066 of the DACcontrol (in dBfs) to hardware bits. In addition, the PLO data table 8067from Power Leveling is part of the overall Attenuation Map 2029, and theoutput must be updated synchronously, as the frequency shifts, withupdates of the output of the attenuation parsing function, according toan exemplary embodiment.

The level shift 8060 maps the absolute power command (dBm) 2031 into arequired relative power (dBfs) 8061, according to an exemplaryembodiment. The Step Attenuator State parsing function 8062 determinesthe appropriate state of the step attenuator, based on the requiredrelative power 8061 and the stored SAAC data table, according to anexemplary embodiment. Once the appropriate step attenuator state 1008 isdetermined, the corresponding SAAC value is subtracted off of therelative power command to yield the residue for the AM DAC (dBfs) 8064,according to an exemplary embodiment.

The Super-Attenuation function 8063 is a quadratic interpolation ofSuper-Attenuation data collected during Amplifier Compression Alignment,according to an exemplary embodiment. Per Amplifier CompressionAlignment, above, the data was collected in three ranges, depending uponthe state of the step attenuator 1014, and the data appropriate to theStep Attenuator State (Output of the Step Attenuator State Parser) 1008must be used, according to an exemplary embodiment. The data may spanthe range from 0 dBfs to −16 dBfs on the SSI AM DAC 1006 for each of thethree ranges. Super-Attenuation data may be directly interpolated overthis range. Most non-linearity occurs with the first few dB ofattenuation, and the Super-Attenuation data will change accordingly. Athigher values of attenuation, the super-attenuation data is essentiallyconstant, and is extrapolated below −16 dB by simply re-using the −16 dBvalue for all higher levels of attenuation, according to an exemplaryembodiment.

The appropriate super attenuation value is added to the AM DAC Residue8064 (Addition of negative dB values), to produce the actual AM DACControl 8065 (Saturation-Compensated, in dBfs), according to anexemplary embodiment.

There are 56 SSI base-bands, used in conjunction with 14 up-converterbands, to produce 603 sub-bands between 0.5 and 22 GHz (Not all possiblecombinations are used), in an exemplary embodiment. All amplitude values(Level Shift, SAAC, & Super-attenuation) are referenced to the center ofthe applicable SSI sub-band, and are assumed to be valid anywhere withinthe sub-band, according to an exemplary embodiment.

Step Attenuator State Parser

The Step-Attenuator State Parsing function 6062 takes a RequiredRelative Power Command (−x dBfs) and computes what state(0-6) of theStep Attenuator is required, according to an exemplary embodiment.

Note: By convention, the relative power command and all attenuationvalues are expressed as negative dB, according to an exemplaryembodiment.

The algorithm for parsing is equivalent to the following:SAtten_State=0;Residue=Cmd;Do[If[Cmd<SAAC_data[[i]],(SAtten_State=i;Residue=Cmd−SAAC_data[[i]])],{i,1,6}];

(* Cmd is assumed to be a negative value, in dBfs. SAAC_data is thearray of 6 SAAC filtered State-Estimate values (negative dB).SAtten_State is the numerical state of the Step Attenuator, 0 to 6,representing nominal 0 to −60 dB, in ten dB steps. Residue is a negativevalue, in dBfs, that captures the additional attenuation required on theScaling DAC *)

DAC Theoretical Code Conversion

The AM DAC Control (dBfs) 8065, according to an exemplary embodiment, isconverted to hardware code on a straight theoretical basis:DAC_Full_Scale=32,768;(*Assumed 16 bit Scale, Bipolar*)DAC_Code=Round[DAC_Full Scale*10^(Residue/20)];

Level Shift

The Level Shift 8060, according to an exemplary embodiment, is afrequency dependent value (1 value per sub-band) that causes the correctabsolute power to be produced at the port output. It is computed suchthat the Base-State Power Command (i.e., −10 dBm commanded) will producean actual output power of −10 dBm. It should be noted that theSaturation-Compensated Base State Power (SCBSP) level used forContinuous Internal Alignment is equivalent to a −10 dBm absolute powercommand with zero Level Shift. Thus, the difference between −10 dBm andthe measured BSA is the required Level Shift at any given frequencysub-band (BSA value will typically be negative dBm):Level Shift=−10 dBm−BSA.

Building the Phase Map

The process for mapping phase is illustrated in diagram 9000 of FIG. 9,according to an exemplary embodiment. Total phase compensation 9075 isthe sum of the Base-State Phase (BSP) 9072, the Step Attenuator PhaseContribution (SAPC) 9071, the Filter-Induced Phase Contribution (FIPC)9073, and the Saturation Induced Phase Contribution (SIPC) 9070, all ofwhich are in units of degrees, according to an exemplary embodiment.

The BSP 9072 is a single value for use anywhere within the sub-band, asis the SAPC 9071, in an exemplary embodiment. The SIPC value 9070 isvalid anywhere within the sub-band, but must be interpolated from storeddata to give the SIPC value that is appropriate for the current settingof the Step-Attenuator 1008 and the command going to the SSI AM DACControl 8065 (SIPC interpolation is exactly analogous to theinterpolation for super-attenuation described above), according to anexemplary embodiment.

FIPC data 9073 must be interpolated to find the FIPC that is specific tothe exact frequency being produced, in an exemplary embodiment. Thisfunction may be interpolated from stored data using quadraticinterpolation and the data groupings defined in Filter-Induced PhaseContribution (FIPC), above.

Once a composite phase compensation 9075 has been computed, this valueis subtracted from the Phase Command 2032 to yield the phase value to beloaded into the SSI 1004, according to an exemplary embodiment.

External Measurement Port Alignment

External Measurement Port Alignment, according to an exemplaryembodiment, uses the “B” Channel of the measurement receiver 2024 tomeasure SSI_(1,1) at the output of Port 1 2021, and correlate thesemeasurements to measurements of the same SSI 1001, under the sameconditions, with a Power Meter 2027. Because the “B” Channel uses thesame LO as the “A” Channel, External Measurement Port Alignment musttime-share access to the measurement receiver with Continuous InternalAlignment, according to an exemplary embodiment.

Instead of sweeping all SSIs 1001 in the system, a special case of theContinuous Internal Alignment Cycle must be established that does thefollowing, according to an exemplary embodiment:

a. Conduct Continuous Internal Alignment Frequency Sweep on SSI_(1,1) (8ms);

b. Conduct 8 ms worth of External Measurement Port Alignment; and/or c.Repeat a & b until External Measurement Port Alignment operation iscompleted.

Note: Continuous Alignment of other SSIs is suspended during thisoperation so that measurement receiver resources may be time-sharedbetween Continuous Internal Alignment of SSI_(1,1) and the alignment ofthe External Measurement Port, according to an exemplary embodiment.

External Measurement Port Alignment, according to an exemplaryembodiment, is a process that aligns the “B” Channel of the measurementreceiver 2023. This operation is a two-step process, according to anexemplary embodiment. First, the amplitude terms for the InternalMeasurement Path (IMP) for SSI_(1,1) (IAACF_(1,1)) are aligned byplacing a power meter 2027 on Port 1 2021, then alternately measuringSSI_(1,1) with the external power meter 2027, and again with theinternal measurement receiver 2023. The amplitude correction factors forIMP_(1,1) are calculated from the difference in the internal andexternal readings. Once the amplitude factors for IMP_(1,1) are known,the power meter is removed, and the movable test cable from the “B”channel of the measurement receiver is connected to Port 1 2021. Themeasurement process is repeated, this time comparing the known readingon the “A” channel (IMP_(1,1)) with the unknown reading on the “B”channel. The “B” channel is aligned by computing the EACF as thedifference between the two readings, according to an exemplaryembodiment.

The process for calibrating the measurement receiver (External “B”Channel), according to an exemplary embodiment, is summarized asfollows:

a. Connect Power Meter to Port 1;

b. Activate Modified Continuous Internal Alignment Cycle;

c. Wait 2 seconds for alignment to stabilize;

d. Set SSI_(1,1) to Sub-band 1 & route to Port 1;

e. Measure power on Power Meter (Using TBD VSWR CancellationProcessing);

f. Switch SSI_(1,1) & Measure with “A” Channel of Measurement Receiver,using VSWR cancellation per Section 3.1.2.2.1. Do not Normalize thismeasurement for path loss;

g. Compute IAACF_(1,1): IAACF_(1,1)=P_(Power) _(—) _(Meter)−P_(Meas)_(—) _(Receiver),

h. Repeat d through g for all 603 sub-bands;

i. Remove the Power Meter from Port 1 and replace with the Channel BMovable Test Cable;

j. Set SSI_(1,1) to Sub-band 1 & route to Port 1;

k. Measure power on B Channel (Using VSWR Cancellation Processing, butdo not Normalize for path-loss);

l. Switch SSI_(1,1) & Measure with “A” Channel of Measurement Receiver,using VSWR cancellation per Section 3.1.2.2.1. Normalize thismeasurement for path loss, using the IAACF_(1,1) value computed above;

m. Compute EACF: EACF=P_(A) _(—) _(Chan,Normalized)−P_(B) _(—)_(Chan, Un-normalized); and/or

n. Repeat j through m for all 603 sub-bands.

Transfer Alignment of Internal Measurement Paths

Transfer alignment, according to an exemplary embodiment, computes theInternal Alignment Amplitude Correction Factor (IAACF) and InternalAlignment Phase Correction Factor (IAPCF) for each SSI 1001, the centerof each sub-band. The IAACF and IAPCF values are computed by correlatingmeasurements of the output port (Obtained from the external measurementport) with measurements from the internal alignment feedback paths,according to an exemplary embodiment. The Continuous Internal Alignmentcycle needs to be running for these measurements, according to anexemplary embodiment. If the system is new and has never been aligned,the IAACF and IAPCF data tables should initially be loaded with defaultvalues (0 dB, 0 Degrees) so that Continuous Internal Alignment, whichuses these values to Normalize measurements, can function, according toan exemplary embodiment. The new values for IAACF and IAPCF will becomputed as an iterative update to the prior data, in an exemplaryembodiment.

Because both the “A” Channel (Internal) and the “B” Channel (External)are used, and both share same LO, the frequency sweep of the SSI beingmeasured externally must be time synchronized with the frequency sweepof the measurement receiver, according to an exemplary embodiment.

The process is summarized as follows, according to an exemplaryembodiment:

a. Connect External Alignment Port Movable Test Cable to Port 1;

b. Activate the Continuous Internal Alignment process and wait 30seconds for the system to stabilize;

c. Rout SSI_(1,1) to Port 1 output, and sweep in frequency in parallelwith the foreground portion of the Internal Alignment Frequency SweepCycle (Base-state amplitude & Phase). Record Normalized Amplitude andPhase Measurements on “B” Channel;

d. Compute Amplitude Error (dB) for each sub-band edge as follows:Amp_Error=Normalized Amplitude_(B Char),+10 dB;

e. Compute Phase Error (dB) for each sub-band edge as follows:Phase_Error=Normalized Phase_(B Chan);

f. Iterate IAACF value (dB) for each sub-band as follows:IAACF_(n+1)=IAACF_(n)+Amp_Error;

g. Iterate IAPCF value (Degrees) for each sub-band as follows:IAPCF_(n+1)=IAPCF_(n)+Phase Error;

h. Repeat steps c thru g for each SSI on port 1; and/or

i. Repeat steps a thru h for each port (2-16).

Time of Arrival Alignment

Time of Arrival Alignment (as shown in diagram 10000 of FIG. 10) hasthree aspects, as follows, according to an exemplary embodiment:

a. Hardware Transfer Function Linearization;

b. Hardware Transfer Function Gain Scaling; and/or

c. System Inter-channel Delay.

All processes are run using a Digital O-Scope 2026 (See FIG. 2) tomeasure the pulse time of arrival of each SSI with respect to aSSI_(1,1) (System Reference), according to an exemplary embodiment.Normally, this is done as a two-channel O-scope measurement, but on Port1, multiple SSIs will appear on the same channel, according to anexemplary embodiment. For Port 1, therefore, it is necessary to measuretiming using the waveform shown in FIG. 10, according to an exemplaryembodiment. As shown, the measurement waveform is a periodic couplet, inwhich the first pulse of the pair is the SSI_(1,1) reference 10002, andthe SSI under alignment is the second pulse 10004 of the pair, accordingto an exemplary embodiment.

Note: When measuring delay characteristics for SSI_(1,1), it can be usedas its own trigger reference, in accordance with the scheme shown inFIG. 10. In this case, both pulses are from SSI_(1,1), the first toserve as a trigger reference, and the seconds to measure programmedincremental delay.

Transfer Function Linearization

There is a table of 1024 values dedicated as the characterization mapfor pulse modulation (PMOD) Fine Delay, according to an exemplaryembodiment. The basic clock resolution for PMOD is 8 ns, but a delayline is used to provide 8 ps interpolation of the 8 ns clock, in anexemplary embodiment. The delay-line has multiple taps, and the taps maynot be perfectly weighted with respect to each other, according to anexemplary embodiment. A purpose of this map is to remove non-linearityand non-monotonicity in the hardware transfer function that results fromimperfect weighting of the various taps, according to an exemplaryembodiment. This alignment is expected to be a one-time-only factorycharacterization, in an exemplary embodiment.

The linearization process, according to an exemplary embodiment, mayinvolve measuring, in steps of 8 ps, the hardware bit pattern requiredto produce the desired delay. This process should be implemented in amanner similar to the iterative search used to map amplifier compression(see Search Algorithm, above), wherein the nominal value is used as aninitial estimate, the actual delay is measured and the error computed,and the estimate is adjusted by the error, according to an exemplaryembodiment.

The resulting data table is the numerical sequence of hardware bitpatterns to produce a linear, monotonic delay characteristic, accordingto an exemplary embodiment. This characteristic data may be stored innon-volatile Flash Memory in each SSI Digital Controller, according toan exemplary embodiment.

Transfer Function Gain Scaling

A purpose of gain scaling, according to an exemplary embodiment, is tokeep the full-scale delay of the interpolating delay line equal to the 8ns clock resolution. (The delay-line elements may change by as much as±2 ns over the range of temperature extremes for a flight-line system.)Gain scaling may be implemented on command, based on significant changein system temperature, according to an exemplary embodiment.

The Transfer Function Linearization characteristic data described aboveis a look-up table that maps a delay command (ps) into a specific bitpattern for the hardware, according to an exemplary embodiment. Thistable is read from the SSI non-volatile flash memory, and is copied intothe Alignment Processing RAM memory when the SSIs are powered-on,according to an exemplary embodiment.

Gain scaling may include requesting a measurement from the SSI(Conducted as an internal clock-management measurement) of the errorbetween the 8 ns digital clock period and the full-scale value of thelinearization characteristic, in an exemplary embodiment. The measurederror is used to scale the address range of the LinearizationCharacteristic so as to build a look-up table that is a properly scaledmapping of delay command (in ps) to actual hardware bit patterns thatwill cause the desired delay, according to an exemplary embodiment.

Alignment of Insertion Delay

Time of Arrival Alignment is a process that measures differences inchannel-to-channel pulse time of arrival between each SSI, and may applytrim compensation if required, according to an exemplary embodiment.Time of Arrival alignment may be run on-command (Not while simulationsare active), according to an exemplary embodiment.

Each SSI has 2 offset registers; one to adjust leading edge delay andthe other to adjust trailing edge delay, according to an exemplaryembodiment. SSI_(1,1) serves as the system reference. The leading edgeregister for this SSI is loaded with a Reference Insertion Delay(Nominally, 16 ns), in an exemplary embodiment. The insertion delay forall other SSIs is aligned as follows:

a. Set Leading Edge Delay (LED) to Reference Delay (16 ns);

b. Measure SSI Under Test pulse timing WRT SR_(1,1);

c. Compute Error: Error=Time_(SSIn)−Time_(SSI1,1);

d. Leading Edge Delay: LED_(n+1)=LED_(n)−Error;

e. Adjust Trailing Edge Delay: TED_(n+1)=TED_(n)−Error; and/or f.Iterate if required.

Note: The purpose of adjusting the Trailing Edge Delay whenever LeadingEdge Delay is adjusted is to ensure that Alignment of Insertion Delaydoes not interact with Pulse Width Alignment, according to an exemplaryembodiment.

Pulse Width Alignment

Pulse Width Alignment, according to an exemplary embodiment, may beimplemented by using a Digital O-Scope 2026 (See FIG. 2) to measure thepulse width of each SSI 1001.

Pulse width is adjusted, if required by programming the Trailing EdgeDelay register, according to an exemplary embodiment. The process is asfollows, according to an exemplary embodiment:

a. Measure SSI Under Test pulse width;

b. Compute Error: Error=PW_(Meas)−PW_(Nominal);

c. Adjust Trailing Edge Delay: TED_(n+1)=TED_(n)−Error; and/or d.Iterate if required.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Thus, the breadth and scope of thepresent invention should not be limited by any of the above-describedexemplary embodiments, but should instead be defined only in accordancewith the following claims and their equivalents.

1. A method for using a “B” channel of a dual channel measurementreceiver as a transfer standard for power measurement comprising:correlating measurements made with an “A” channel to measurements madewith an RF Power Meter on one RF signal source, so that readings fromthe “A” channel are aligned to the RF Power Meter; aligning the “B”Channel to the “A” Channel (Transfer alignment of Channel B to the RFPower Meter), once the “A” channel has been aligned to read the same asthe RF Power Meter; and using the “B” Channel as a transfer standard tomeasure all remaining RF signal sources in the system, on a time-linemuch faster than may be accomplished using a power meter.